A peptidase in human platelets that deamidates tachykinins. Probable identity with the lysosomal "protective protein".

摘要: We discovered an enzyme in human platelets that deamidates substance P and other tachykinins. Because amidated carboxyl terminus is important for biological activity, we purified characterized this deamidase. The enzyme, released from by thrombin, was to homogeneity ammonium sulfate precipitation, followed chromatography on octyl-Sepharose column chromatofocusing PBE 94. exhibits esterase, peptidase, deamidase activities. peptidase activity (with furylacryloyl-Phe-Phe) optimal at pH 5.0 while the esterase (benzoyl-tyrosine ethyl ester) (D-Ala2-Leu5-enkephalinamide) activities are 7.0. With biologically peptides, acts both as a (substance P, neurokinin A, eledoisin) carboxy-peptidase bradykinin, angiotensin I, P-free acid, oxytocin-free acid) neutrality, although carboxypeptidase action faster 5.5. Enkephalins, upon deamidation of enkephalinamides, were not cleaved. Gly9-NH2 oxytocin without deamidation. Peptides with penultimate Arg residue hydrolyzed. Some properties similar those reported cathepsin A. inhibited diisopropylfluorophosphate, inhibitors chymotrypsin-type enzymes, mercury compounds catheptic trypsin-like metalloproteases ineffective. In gel filtration, native has Mr = 94,000 non-reducing sodium dodecyl sulfate-polyacrylamide electrophoresis 52,000 indicating it exists dimer. After reduction, dissociates into two chains 33,000 21,000 determined electrophoresis. [3H]diisopropylfluorophosphate labeled active site serine chain. first 25 amino acids sequenced. They identical sequences lysosomal "protective protein" which, turn, sequence similarity KEX1 gene product Y yeast. This protective protein complexes beta-galactosidase neuraminidase lysosomes vitally maintaining their stability. A defect cause galactosialidosis, severe genetic disorder. ability physiological stimuli (e.g. thrombin or collagen) release indicates may also be involved local metabolism bioactive peptides.